As disclosed in Patent Literature 1 (Japanese Patent Laid-Open No. 2007-224878), for example, a fuel supply system for an internal combustion engine using an alcohol fuel according to a prior art has been known. The alcohol fuel is hard to vaporize particularly at low temperature, so that the conventional internal combustion engine has a vaporizing chamber for vaporizing the fuel at the start of the engine. The vaporizing chamber has an enclosed structure sealed from the outside and is connected to an intake air channel via a throttling channel. The vaporizing chamber is provided with a start fuel injection valve for injecting the fuel into the chamber and a heater for heating the injected fuel.
At the start of the internal combustion engine, the heater is first activated when a start signal is provided to the internal combustion engine, and then, the fuel is injected into the vaporizing chamber through the start fuel injection valve after a lapse of a certain time. When the fuel is injected into the chamber, the vaporizing chamber is in a decompressed state because of an intake air negative pressure due to cranking. Thus, the injected fuel is vaporized by the heat from the heater in the vaporizing chamber in the decompressed state, and the vaporized fuel is supplied to each cylinder through the intake air channel. In this way, according to the prior art, at the start of the engine, the fuel is vaporized in the vaporizing chamber to secure the startability in cold start or the like.
As literatures relating to the present invention, the applicant has been aware of the following literatures including the literature described above.